As best we can tell, humans and Neanderthals diverged from a common ancestor about 500,000 years ago, a species called Homo heidelbergenesis. Modern humans appeared in Africa some 300,000 years later, a time when Neanderthals were already romping around Europe and Asia.

These skulls are 430,000 years old. They have a small braincase but in other respects have Neanderthal characteristics.

…the Neanderthal trait of an elongated and rounded brain case came later.

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Placoderms are an extinct class of armoured fishes containing several orders. Placoderm comes from Greek words for “plate” and “skin.” They are jawed fishes, but so ancient that they precede both sharks & rays and bony fishes: some elements of the skeleton are cartilaginous while others are bony and there are bony elements in their skin armour. Yes, bones and teeth are derived from skin tissue. They appeared in the fossil record about 420 Ma in the Early Silurian and by 400 Ma in the Devonian all major placoderm orders were present. (See “Australia: The Land Where Time Began: Placoderms“.}

Before placoderms, all fertilization of eggs by sperm occurred outside the body, as females released eggs and males released sperm into the water. They might hover near each other, but if sperm found egg it was partly by chance. Female fishes release their eggs through a cloaca, an opening for both eggs and bodily wastes. As the fish that were closest had the most success, eventually males began to position themselves at the cloaca. One group of placoderms, the ptyctodontids, have these external claspers to hold the female, as do sharks. The pelvic fin perhaps developed a tube shape to funnel the male’s sperm into the female’s cloaca. Some modern fish mate in this way. What is known is that some placoderms gave birth to live young, which means that that at the very least, eggs were fertilized while still in the female. In short, these early fishes invented internal fertilization.

There are two pathways after internal fertilization. One is ovivipary, where eggs are retained and hatch inside the mother, who then expels the young. Some sharks still do that. In fact, in some sharks the first young to hatch eat the other eggs to nourish themselves until birth. Females may develop areas of nourishing skin that the young can scrape off. The other main path is for the young & the female to cooperatively grow a placenta, which attaches to the her and extracts nourishment from her blood. (Placentas could not have happened without a retrovirus inserting itself into the genome, but that’s another topic.)

At first, scientists thought that young placoderms inside larger fossils could have been evidence of predation; but at last a tiny fossil placoderm was found with a tiny umbilical cord, still attached to the mother.

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There are some arguments based on misunderstanding of how words are used in science, or deliberate mis-use by creationists. Just as Microsoft Windows is different from house windows, so in science “theory” means well-tested explanation, not a notion. Hypothesis means explanation that can be tested, not wild-assed guess. Here are seven science words that we need to learn, or perhaps that scientists should simply stop using. I’m in favour of replacing “theory of evolution” with “explanation of the mechanics of evolution” to start with:

“My research involves comparisons of independent evolutionary transitions such as convergence, parallelism, duplication, and homoplasy. Such transitions provide an element of replicability within the singular history of life, and can yield insight into the most general evolutionary questions. For example, when and why do the same molecular or developmental changes underlie similar – though independent – evolutionary changes? What are the fates of duplicated genes, and what causes them to diversify or retain old functions? How can we even determine what is an independent evolutionary event?”

One of his students has discovered that chitons have eye lenses made of aragonite, which is the material used by trilobites.

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Check out the reaction and link fest at Jeremy Voder’s Denim and Tweed: Evol2012.

All in all, I had a great time, and saw a lot of really cool science. This was the first Evolution meeting I’ve been to where I was never at a loose end—every moment I was in the Convention Centre, I had someone to go see, or a talk to go hear. And, honestly, I finished the meeting without having checked in with everyone I’d have liked to.

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A tiny trackway discovered in sedimentary rock has pushed back the date of the first organism capable of walking to 585 million years ago. This proof is 30 million years older than previously known evidence.It took two years to precisely date the trackway by radiometric dating of igneous rock that intruded into the sedimentary rock. The fossil was found in Uruguay.

The organism was about the size of a grain of rice. A trackway like this shows that it had front and back ends and was bilaterally symmetrical, with limbs that could move it forward. We could call it First Explorer.

Eucritta melanolimnetes represents ancestral tetrapods. We mammals did not descend from amphibian: we descended from reptiles. The Amphibians are on a separate branch of the family. Eucritta has features of both. It is a transitional form, vulgarly called a “missing link.” But obviously it’s not missing. Described by Jennifer Clack in 1998, it’s from the early Carboniferous Era.

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The Out Campaign

“Atheism is a religion like 'not collecting stamps' is a hobby.”
―Penn Jillette“If atheism is a religion, then bald is a hair color” ―Mark Schnitzius"If atheism is a religion, then health is a disease!" —Clark Adams